Circular Deformations

The brain can alter the apparent shape, depth, and motion of spinning patterns. At this art piece by Fred and Ellen Duncan  visitors observe different spinning disks and see slightly different illusions. When the disks are still, it is apparent that the pictures are multicolored, two-dimensional images. When spinning, they all appear three-dimensional. Our brains are always working to make sense of the visual world. This can be a difficult job, especially when what is seen is strange or unfamiliar. For example, our brains do not know quite what to make of a spinning black ellipse, one of the images on the disks. Spinning ellipses are rarely seen in nature. On the other hand, tilted circles which look exactly the same as ellipses, are familiar. Our brains decide that tilting circles make more sense than spinning ellipses, and so the image appears as a circle tilting out of the disk.

Depth Spinner

At this exhibit, visitors spin a disk with a black and white spiral pattern on it. While spinning, there stare at it for fifteen seconds. When they look up at a blank wall, they notice the wall seems to be moving. Specific mechanisms in your eye and brain detect inward and outward motion. When something is standing still, the receptors detecting inward motion are in balance with the receptors detecting outward motion. When you stare at this moving pattern, one set of motion detectors gets tired. When you look at the wall, the motion detectors that haven't been working override the tired ones, and you see motion in the opposite direction. When you spin the disk so that the spiral seems to be moving away from you, the wall will seem to be moving towards you. When you spin the disk in the opposite direction, the spiral will seem to move toward you and the wall will seem to be moving away from you.

Distorted Room

When visitors look into this room through a view hole, it appears to be an ordinary rectangular room. But a person walking back and forth across the room appears to shrink and grow. This illusion occurs because the shape of the room is far from rectangular. The walls on the left side of the room are significantly undersized, and other features of the room taper uniformly from the full sized walls on the right side to the reduced one on the left side. Since we live in rectangular rooms, we tend to interpret the distorted room as if it were rectangular. In the distorted room, persons in the far left corner are actually further away then they would appear in a rectangular room. They therefore seem smaller than they are.

Far Out Corners

In many cases, how humans see the world is based on past experiences and general perceptions. The idea and sight of a box can be pretty clear cut, and most people immediately identify a "box" pretty quickly. This exhibit challenges visitors by presenting a series of suspended white squares that seem to form a cube where they meet, pointing away from the viewer. As the viewer moves side to side in front of the exhibit, the "cubes" seem to turn to follow the visitor. But it is all an illusion created by fooling the brain with some paper squares and proper lighting.

Old Woman or Young Lady?

This illustration was created by cartoonist W.E. Hill, and was originally published in 1915 as “My Wife and My Mother-in-law.” Psychologists have been using it since the 1930s to demonstrate something called “multi-stability in perception,” which basically means you may see it as one thing or the other. This illusion is a perceptual illusion in which the brain switches between seeing a young girl and an old woman. Look at this classic 19-centrury illusion, and you’ll do a double-take. The mature woman’s prominent nose can also be a young girl’s face in profile. The woman’s thin-lipped smile can become the young girl’s choker-collar.

Reverse Masks

In this exhibit, two masks (plaster heads) are mounted side by side. They appear identical when viewed with one eye from a distance of more then ten feet. But, when visitors walk back and forth while watching the masks, the mask on the right appears to rotate, following visitors movement. Upon closer inspection, visitors see that the mask on the right is inside out or concave. Since we are used to seeing faces that protrude outward, our brain tends to assume that both masks are ordinary protruding faces, even though the mask on the right is actually a hollow impression of a face. When visitors move counterclockwise around the concave mask, they do not expose any portion of the masks they did not see before. The brain tries to present an interpretation of the experience that makes sense based on previous experiences. It therefore interprets the mask as an ordinary protruding face that turns to watch visitors walk past.

Sliding Gray Step

This exhibit demonstrates an interesting problem in the area of perception. Normally the brightness of an object is perceived relative to the brightness of objects around it. A gray object should appear lighter when surrounded by darker objects and darker when surrounded by lighter objects. At this exhibit visitors slide a gray striped panel over a black and white striped panel to discover that the exact opposite is true. This illusion is not fully understood, but it seems to have something to do with the way the eye determines relative shading.

Squirming Palm

Visitors turn a knob to make a disk spin slowly. Staring at the spinning disk for 15 seconds, and then staring into the palm of the hand, visitors notice that their palm seems to be turning in the opposite direction from the way the disk was spinning. When we stare at a moving pattern, our eyes and brain get used to seeing movement. When we look at something that's standing still, our eyes see movement in the opposite direction. The common name for this illusion is the waterfall effect. If you stare at a waterfall for some time and then look at nearby rocks, the rocks appear to be moving upward.

Trapezoidal Window

Sometimes we see only what we expect to see. In this exhibit an apparently rectangular window appears to swing back and forth. Visitors stand a few feet away, close one eye and observe the window. Upon closer examination with both eyes open, visitors discover that the window is actually rotating. Upon even closer inspection, visitors notice that one vertical edge of the window is shorter than the other. Most windows are rectangles, but this window is a trapezoid. When a rectangular window is angled away, however, its further edge appears smaller. Because of past experience, the brain assumes that the window in this exhibit is rectangular, and that one edge appears smaller only because it is further away. But one edge of the window is smaller. When this smaller edge moves closer to the observer, the brain refuses to see it as being closer. Instead, it assumes that the window is now rotating in the opposite direction. The window therefore appears to swing back and forth.

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